03 Ram 3500 shortbox quad tire issues

Your 3" lift will cause the axle to sit further rearward in the wheelwell. Unless you put longer control arms on. This is probly your problem. A 2" kit with stock control arms will clear 315's on stock wheels. But a 3" kit on stock control arms may be to much. Probly hafta lose the mudflaps also.

If you have the Mopar molded mudflaps, there is no relocating them.

Since you have stock rims, and a 3" lift. I ASSUME that control arms will fix your problem.
Did your lift come with arms? Is it a lift or a 3" leveling kit?

Do you have a adjustable track bar? That'll be about next on the list.

If your control arms are red, then they've already been changed. Do you have a spacer ontop of the coils or not?

Sad to say, but you may be farther ahead to remove whatever spacer is on your truck currently, measure it, and puting it back on your truck. Then you will know what your truck has on it. A adjustable track bar wouldn't hurt anything either. I have 2" spacers on my truck, with a adjustable track bar, and run 35x12.50 BFG MT's on H2 wheels and have 0 clearance issues. Without a adjustable track bar, 315's on stock wheels will have a little rub on the passenger side control arms due to the axle being shifted towards the drivers side with a 2" leveling kit. Most don't worry about it and just learn to not turn so short when turning right. But the adj. track bar will correct this.

The tubing under the bed is probly not a body lift. Look where the bed actually bolts to the frame mounts. Is there a cylinder shaped plastic spacer? About 3" tall? If it has a body lift, there will be these cylinder shaped spacers everywhere the body mounts to the frame. Front and rear. Not just the bed. I'm pretty sure you don't have a body lift.

As far as front coil spacers, sounds like a typical poly (plastic) spacer. Generally 2".

Back to control arms, the 3rd gen control arms are not U or C shaped. They are more of a rectangular tube. 2nd gen trucks had the U or C shaped arms. They boxed the arms in on the 3rd gens. Are your arms Round tube or more like I described? Any way you can just take pics for us? Would be MUCH easier to help you.

Yeah. That's what I thought. They are probly the stock arms. Did the tire place tell you exactly why the 315's won't fit? I'm curious. Cause everything you've told me so far, leads me to believe that they will. If you can't get the pics to post up, just email them to me at [email protected] and I'll take a look and see what I can figure out.